While it is quite commonplace to find a variety of beverage insulators that are configured to securely hold a substantially cylindrical cup or glass, such beverage insulators are typically not adequately adjustable and do not accommodate mugs with handles or the like. Mugs with handles are ubiquitous in most households and workplaces today. Most conventional adjustable beverage insulators are simply made of a resilient material, include one or more expansion slots or the like, and/or make no accommodation for the handle of a mug or the like, or include cumbersome straps that are designed to pass through or around the handle of a mug or the like. As a result, these conventional adjustable beverage insulators simply do not work very well and have limited utility. Thus, what is still needed in the art is an improved adjustable beverage insulator that is configured to securely hold a substantially cylindrical cup, glass, mug with a handle, or the like.